The present invention relates to a low-frequency power amplifier, particularly to a direct-coupled power amplifier connected in a bridged configuration.
A direct-coupled power amplifier connected in a bridged configuration, in other words, a bridged transformer less power amplifier (BTL power amplifier) comprises main and inverse amplifier units having the same constitution but producing an inverted output from each other. A low impedance load, such as a loudspeaker, is directly connected between the output ports of the main and inverse amplifier units.
If outputs appear from the main and inverse amplifier units and, furthermore, if the phases of the outputs are different from each other, as shown by the solid and broken lines in FIG. 1a, at a time when the power supply is initiated, pulse signals corresponding to the difference in the voltage, as shown in FIG. 1b, are applied to the loudspeaker. Thus, transitional noises, such as so-called "pop noises" are heard often from the loudspeakers when the power is applied.